Natural History
The American bullfrog is a warmth loving species that seems to be near the northern limits of its physiological tolerance in southern British Columbia. Consequently, it is the last amphibian species to emerge from winter torpor and it will not reproduce until water temperatures are well above 20 degrees Celsius in mid-summer. All life stages generally overwinter in the water, where they remain at the bottom of lakes and ponds until warmer water temperatures return in the following spring.
The egg stage is very brief. Tadpoles may take 2 to 4 years to reach metamorphosis at this latitude. Juveniles will often leave lakes on rainy nights and venture off to colonize new lakes. Adults are cannibalistic, and juvenile bullfrogs can form a large part of the adult diet.
A very large mouth and powerful hind legs combine to make adult American bullfrogs formidable predators, and they will eat a huge variety of organisms. Recorded in their diet are earthworms, leeches, insects, centipedes, millipedes, spiders, crayfish, snails, salamanders, tadpoles, frogs (including juvenile bullfrogs), fish, small alligators, small turtles, lizards, snakes, shrews, moles, mice, bats, and birds - including baby ducks and forest birds the size of robins and orioles.
Many native species are easy prey for American bullfrogs, including listed species such as the hatchling painted turtle in the accompanying photo. For the first year of a turtle’s life it is just bite-sized for a bullfrog.
Two species of native garter snakes - Common Garter Snake (Thamnophis sirtalis) pictured below, and the Western Garter Snake (Thamnophis elegans) - are might be effective predators of juvenile bullfrogs and their tadpoles. However, juvenile garter snakes are also easy prey for adult American bullfrogs.
